Chinese Patent Application No. 200810038254.7, titled as a new external fixation system for orthopedics, a using method thereof, and a polyurethane for the fixation system, has disclosed a polyurethane for an external fixation system for orthopedics. However, in poor conditions, for example, in the field at a low temperature, where no hospitals are available, and the temperature is about 5-15° C., the fixation system cannot be hardened by the polyurethane; whereas in the temperature of 25-30° C., the hardening of the fixation system is too fast and produces too much heat.